Q1. The revision denotes the hardware configuration at the time of manufacture. Having an earlier or later revision doesn't mean something is wrong or you are missing features. Manufacturers purchase components in bulk. Then build thousands of boards. If they need to build more and the same components cannot be sourced, a new MB revision is created. This way a manufacturer can keep track of the components that the board was assembled with. Board revisions can also be made to correct issues, but this is less common.
Q2. Do not upgrade for the sake of having the latest BIOS. If what you have is working, stick with it.
Q3. Purchase RAM that is on the QVL for your board. This helps to ensure compatibility.
Rev 1.0
http://download.gigabyte.us/FileList/Memory/mb_memory_x79-series.pdfRev 1.1
http://download.gigabyte.us/FileList/Memory/mb_memory_x79-series.pdfI think they are the same, but use the one for your board's rev as reference. Sadly these are old and outdated.
X79 chipsets are finicky when it comes to RAM. Your CPU supports DDR3 1333/1600/1866, but sometimes the BIOS can have issues with higher density RAM modules. The RAM you have chosen might need to be configured manually if XMP profiles do not work. DDR3-1866 CL10-11-10 @1.5V